A fluorogenic substrate for angiotensin-converting enzyme in plasma

A simple, sensitive, and reproducible assay for angiotensin-converting enzyme is described. It is based on the hydrolysis of the minimally fluorescent substrate p-nitrobenzyloxycarbonylglycyl-L-tryptophylglycine to the products p-nitrobenzyloxycarbonylglycine and the highly fluorescent L-tryptophylglycine. The L-tryptophylglycine was analyzed by fluorometry (lambda excitation = 285 nm; lambda emission = 350 nm). The mean value for human plasma (serum) is 16.5 nmol of substrate hydrolyzed per minute per milliter of plasma under the described assay conditions.